A New Analytical Expression to Estimate the Bending Stiffness of Flexible Risers

2003 ◽  
Author(s):  
Roberto Ramos ◽  
Celso P. Pesce ◽  
Clo´vis A. Martins
Keyword(s):  
Elastic Behaviour ◽  
Flexural Stiffness ◽  
Loop Formation ◽  
Structural Behaviour ◽  
Element Analysis ◽  
Flexible Risers ◽  
Linear Elastic Behaviour ◽  
Ocean Environment ◽  
Critical Regions ◽  
Offshore Oil

Flexible risers are complex structures used in offshore oil exploitation activities. Such structures are composed of several concentric polymeric and steel armour layers which withstand static and dynamic loads applied by the floating production vessel and by the ocean environment. Determining the equivalent flexural stiffness of such structures is an important task for the global structural analysis, since it provides a probable value that can be used in this analysis to predict the load distribution along the line (that is important in critical regions such as the TDP and the top). Besides that, estimates for the flexural stiffness are also important for predicting instabilities in the line (loop formation). However, the complexity imposed mainly by geometry and contact conditions renders a finite element analysis of these structures practically unfeasible, even considering that all the materials obey a linear elastic behaviour. So, in order to achieve this task, analytical methods have been proved to be, till now, a better choice. The aim of this work is to present the basis of a new analytical equation to estimate the flexural structural behaviour of flexible risers. Emphasis is given on the geometrical analysis of armour layers.

A Consistent Analytical Model to Predict the Structural Behaviour of Flexible Risers Subjected to Combined Loads

2002 ◽  
Author(s):  
Roberto Ramos ◽  
Celso P. Pesce
Keyword(s):  
Analytical Model ◽  
Elastic Behaviour ◽  
Structural Behaviour ◽  
Element Analysis ◽  
Technical Literature ◽  
Combined Loads ◽  
External Pressures ◽  
Flexible Risers ◽  
Linear Elastic Behaviour ◽  
Ocean Environment

This work presents an analytical model for the structural analysis of flexible risers subjected to combined loads of bending, twisting and tension, as well as internal and external pressures applied to the riser. Flexible risers, either umbilical cables or flexible pipes, are complex structures used in offshore oil exploitation activities. Such structures are composed of several concentric polymeric and steel armour layers, which withstand static and dynamic loads applied by the floating production vessel and by the ocean environment. The complexity imposed mainly by geometry renders a finite element analysis of these structures practically unfeasible, even if we are to consider that all the materials obey a linear elastic behaviour. So, in order to calculate the stress distribution in the layers, as well as axial, torsional and flexural stiffness values of these structures, analytical methods have been proved to be, till now, a better choice. Using sets of equations, which comprise equilibrium conditions, constitutive equations and geometrical relations, it is possible to solve the problem for all the unknowns. This paper presents a consistent and comprehensive formulation leading to the solution in terms of stresses and deformation components in a flexible riser subjected to the above mentioned combined loads. It is based on the assumption of full-slip of the helically armoured layers after bending is imposed to the pipe. Other main modeling hypotheses are also highlighted in this work. The presented analytical model is, therefore, rather comprehensive and recovers, asymptotically, many results previously published in the technical literature. Comparisons between analytical results using the full-slip model and experimental results obtained in literature are shown and discussed. Some proposals leading to improvement of the presented model are drawn in the conclusions.

Generalised Beam Theory (GBT) for Shear Deformable Stiffened Sections

2014 ◽  
Vol 553 ◽  
pp. 600-605
Author(s):  
Gerard Taig ◽  
Gianluca Ranzi
Keyword(s):  
Cross Sections ◽  
Beam Theory ◽  
Element Model ◽  
Elastic Behaviour ◽  
Structural Behaviour ◽  
Thin Walled ◽  
Shell Finite Element ◽  
Linear Elastic Behaviour ◽  
Generalised Beam Theory ◽  
Shear Deformable

A Generalised Beam Theory (GBT) formulation is presented to analyse the structural behaviour of shear deformable thin-walled members with partially stiffened cross-sections located at arbitrary locations along their length. The deformation modes used in the formulation are taken as the dynamic eigenmodes of a planar frame representing the unstiffened cross-section. Constraint equations are derived and implemented in the GBT member analysis to model the influence of rigid stiffeners on the member response. The accuracy of the approach is validated against a shell finite element model developed in Abaqus. A numerical example describing the linear elastic behaviour of partially stiffened thin-walled member is provided to outline the usability and flexibility of the proposed method.

Lifetime Prediction of Components Including Initiation Phase

2006 ◽  
Author(s):  
Michael Besel ◽  
Angelika Brueckner-Foit
Keyword(s):  
Input Data ◽  
Local Stress ◽  
Fatigue Loading ◽  
Computer Code ◽  
Lifetime Distribution ◽  
Element Analysis ◽  
Initiation Phase ◽  
Mechanics Model ◽  
Critical Regions ◽  
Local Stress Field

The lifetime distribution of a component subjected to fatigue loading is calculated using a micro-mechanics model for crack initiation and a fracture mechanics model for crack growth. These models are implemented in a computer code which uses the local stress field obtained in a Finite Element analysis as input data. Elemental failure probabilities are defined which allow to identify critical regions and are independent of mesh refinement. An example is given to illustrate the capabilities of the code. Special emphasis is put on the effect of the initiation phase on the lifetime distribution.

scholarly journals Extracting real-crack properties from non-linear elastic behaviour of rocks: abundance of cracks with dominating normal compliance and rocks with negative Poisson ratios

2017 ◽  
Vol 24 (3) ◽  
pp. 543-551 ◽  
Author(s):  
Vladimir Y. Zaitsev ◽  
Andrey V. Radostin ◽  
Elena Pasternak ◽  
Arcady Dyskin
Keyword(s):  
Experimental Data ◽  
Poisson Ratio ◽  
A Priori ◽  
Elastic Behaviour ◽  
Crack Model ◽  
Normal Compliance ◽  
S Wave ◽  
Linear Elastic ◽  
Non Linear ◽  
Linear Elastic Behaviour

Abstract. Results of examination of experimental data on non-linear elasticity of rocks using experimentally determined pressure dependences of P- and S-wave velocities from various literature sources are presented. Overall, over 90 rock samples are considered. Interpretation of the data is performed using an effective-medium description in which cracks are considered as compliant defects with explicitly introduced shear and normal compliances without specifying a particular crack model with an a priori given ratio of the compliances. Comparison with the experimental data indicated abundance (∼ 80 %) of cracks with the normal-to-shear compliance ratios that significantly exceed the values typical of conventionally used crack models (such as penny-shaped cuts or thin ellipsoidal cracks). Correspondingly, rocks with such cracks demonstrate a strongly decreased Poisson ratio including a significant (∼ 45 %) portion of rocks exhibiting negative Poisson ratios at lower pressures, for which the concentration of not yet closed cracks is maximal. The obtained results indicate the necessity for further development of crack models to account for the revealed numerous examples of cracks with strong domination of normal compliance. Discovering such a significant number of naturally auxetic rocks is in contrast to the conventional viewpoint that occurrence of a negative Poisson ratio is an exotic fact that is mostly discussed for artificial structures.

scholarly journals Influence of the concrete strength and the type of supports on the stress-strain state of a hyperbolic paraboloid shell footbridge structure

2021 ◽  
Vol 17 (4) ◽  
pp. 379-390
Author(s):  
David Cajamarca-Zuniga ◽  
Sebastian Luna
Keyword(s):  
Thin Shell ◽  
Strain State ◽  
Concrete Strength ◽  
Design Parameters ◽  
Live Load ◽  
Structural Behaviour ◽  
Stress Strain ◽  
Hyperbolic Paraboloid ◽  
Element Analysis ◽  
Stress Strain State

Relevance. This work is the first in a series of publications on the selection of a suitable analytical surface for implementation as a self-supporting structure for a thin shell footbridge. The study on the influence of concrete strength, live load position and support types on the stress-strain state of a hyperbolic paraboloid (hypar) shell is presented. Objective - to define the initial design parameters such as the appropriate concrete strength and the support type that generates the best structural behaviour to perform the subsequent structural design of a thin shell footbridge. Methods. The static finite element analysis was performed for 4 compressive strengths of concrete (28, 40, 80, 120 MPa) which correspond normal, high and ultra-high resistance concrete, 5 different live load arrangements and 3 different support conditions. Results. The shell model with pinned (two-hinged) supports shows the same vertical displacements as the model with fixed supports (hingeless). For the studied shell thickness, in terms of stress behaviour, the model with pinned ends is more efficient. The combination of two-hinged supports with 80 MPa concrete strength shows a better structural performance.

scholarly journals The Analysis with Finite Elements of the Elasto-plastic Behaviour of the Spinal Immobilizers - in the Case of Comminutive Fractures

2019 ◽  
Vol 57 (2) ◽  
pp. 253-264
Author(s):  
Bogdan Florin Toma ◽  
Constantin Nanu ◽  
Cezar Popescu ◽  
Razvan Vladimir Socolov ◽  
Vasile-Eduard Rosu ◽  
...  
Keyword(s):  
Theoretical Study ◽  
Initial Position ◽  
The Body ◽  
Elastic Behaviour ◽  
Element Analysis ◽  
Clinical Observations ◽  
Clinical Investigations ◽  
Extension Force ◽  
Bone Fragments ◽  
Tension State

In this paper it is presented a comparative theoretical study - performed by finite element analysis (FEA), of the tension state that appears at the level of the spine, as well as in the areas adjacent to it, under the following conditions: a) the existence of a comminutive fracture at the level of the vertebra T11; b) of the external immobilization of the body through a Lombax orthesis (LO) or of the internal immobilization of the column by means of a spinal fixator (SF); c) of performing some basic flexion or extension movements. In this study, both flexural force and extension force varied on three levels. The results of the comparative theoretical study were supplemented with the clinical observations obtained from a number of 52 patients who had suffered comminutive fractures in the T11 vertebra and who were treated - by external immobilization, in the Lombax orthesis or were surgically treated - by applying a trapped spinal fixator on the T10-T12 vertebrae. The study had demonstrated that, by immobilizing the body in the Lombax orthesis, following the application of the flexion or extension movement, the mobility of the body is low, the bone fragments move less distances by about 12% against to their displacement under the condition of immobilizing the column by a spinal fixator. Although, in the latter case, the displacements of the bone fragments are greater, the elastic behaviour of the spinal fixator determines the returning of the fragments and of the spine to the initial position as well as the distance between the vertebrae. Clinical investigations on patients treated by external immobilization of the body in the Lombax orthesis show that the values of the local kyphosis angle (LKA) are about 30% lower than the values of the same parameter obtained under the surgical treatment.

Finite Element Analysis of the Thermal Residual Stresses of Diamond Cutting Tools in the Sintering Process

2008 ◽  
Vol 587-588 ◽  
pp. 695-699 ◽  
Author(s):  
Luís G. Reis ◽  
Pedro M. Amaral ◽  
Bin Li ◽  
Carlos A. Anjinho ◽  
Luís Guerra Rosa ◽  
...  
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Diamond Tool ◽  
Diamond Particle ◽  
Elastic Behaviour ◽  
Tensile Behaviour ◽  
Sintering Process ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Thermal Residual Stresses

The main objective of the present work is to present and discuss the effects of the residual stresses generated in the matrix. Both, elastic and elastic-plastic models using explicit finite element code Abaqus were developed to investigate the thermal residual stresses generated around a diamond particle embedded in a metal matrix (a binder) during the sintering process for obtaining a diamond tool. The first part of the work consists in examining the thermal residual stress field generated by using three sintering temperatures from which the bodies are cooled from (T1=800°C, T2=700°C and T3=600°C) and two diamond shapes modelled with 2D axisymmetric elements, one from a circle the other from an octagon, respectively. In this case only one type of binder showing typical elastic behaviour is considered. The second part of this work consists in comparing the finite element solutions using binders with different tensile behaviour (elastic vs. elastic-plastic behaviour). This last study has used a particle shape generated from the octagon, since this shape allows, in a great number of real situations, the simulation of a particle with a larger number of facets, in line with what it is observed when looking at a conventional diamond tool.

Analysis and Design of Offshore Pile Foundation

2014 ◽  
Vol 891-892 ◽  
pp. 17-23 ◽  
Author(s):  
Sudip Basack
Keyword(s):  
Pile Foundation ◽  
Complex Loading ◽  
Offshore Structures ◽  
Laboratory Model ◽  
Element Analysis ◽  
Analysis And Design ◽  
Theoretical Investigations ◽  
Experimental Laboratory ◽  
Combined Action ◽  
Ocean Environment

The ocean environment necessitates the pile foundation supporting the offshore structures to be designed against cyclic load, moments and torques initiated by a combined action of waves, wind, tides, currents, etc. Such a complex loading condition induces progressive degradation in the pile-soil interactive performance introducing significant reduction in bearing capacity with increased settlement and displacements. The Author has carried out extensive experimental (laboratory model tests) and theoretical investigations (boundary element analysis) to study the salient features of this degradation and developed a design methodology for offshore pile foundation. The works conducted and the major conclusions drawn are highlighted in this paper.

Sensitivity Investigation of Specimen Shape on Elastic Behaviour of Perforated Plate

2009 ◽  
Author(s):  
Chang-Hoon Ha ◽  
Tae-Jung Park ◽  
Moo-Yong Kim ◽  
Kwang-Sang Seon ◽  
Jae-Mean Koo ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Perforated Plate ◽  
Type Specimen ◽  
Elastic Behavior ◽  
Elastic Behaviour ◽  
Element Analysis ◽  
Bending Tests ◽  
The Finite Element Analysis ◽  
Specimen Shape

There are various types of tube support plates installed in a steam generator according to the component designer’s preference. Most widely used types of tube support plates are BTSP (broached tube support plate), ATSG (advanced tube support grid), and the eggcrate. In this study, trefoil BTSP specimens made of ASME stainless steel are analyzed and tested. This study is to investigate the effect of specimen shape on an elastic behavior of trefoil BTSP through the compression and bending tests. Prior to the compression and bending tests of BTSP specimens, the equivalent elastic properties of BTSP unit cell are analyzed by the finite element analysis according to the different loading orientation as well as size of the model. Autodesk® Inventor™ software was used to make an analytical model and ANSYS® software was used for the finite element analysis and post-processing. Five and three different shapes of trefoil BTSP specimens are machined and utilized for the compression and bending (4-point and 3-point side bending) tests, respectively. Through the finite element analyses, compression, and bending tests, the equivalent elastic modulus of trefoil BTSP specimen is suggested to be 6,254MPa (907ksi) and the equivalent Poisson’s ratio as 0.64. Specifically the CS5 type specimen which has a ratio of one-fourth (= width/length) was revealed as an appropriate shape of specimen to show those elastic behavior.

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